Lesqucreux.] 4:i-j j^jan 5 



knowledge inchules, with tlieacquaintanceof the greatest number of species 

 recognized at a peculiar locality, that of their mode of dispersion over wide 

 areas, or of the changes caused locally by the geographical distribution 

 of the species. When the coal beds are, tiierelbre, at great distances, it is 

 not possible to leave oft' the idea that the m:)dification8 in the characters of 

 the plants, if diHerences are observed, may have been caused as well by 

 local syuclironous inHuences as by a difference in the time of their f )rma- 

 tion or in their age. Nevertheless, I still believe that in basins of limited 

 areas or for beds of coal of one and the same locality, the remains of plants 

 in the roof shale may serve to identify the different s rata, and may thus 

 be used as a direction by the miners. But even in such cases the paleonto- 

 logical indications may fail or lead to mistakes ; for the changes in the 

 constituents of the roof shales are often sudden and remarkably varied. The 

 Cook vein of Wes'ern Kentucky, for instance, has in its shale a profusion 

 of remains of Lephlodendron and Lepidontrobi on one side of the main 

 gangway, while on the otlier it is transformed into a kind of compact bone 

 or cannel coal with no oiher fossils but small shells. 



When tlie subject of tlic vertical distribution of the vegetation of the 

 coal is considered 11 priori, it seems rational to admit that the same vege- 

 table types cannot have been persistent for such a period of time as was 

 necessary not only for the growth and accumulation of the plants which 

 have entered into the composition of a coal bed from si.v to ten feet thick, 

 or more, but for the heaping of the intercallated strata, sandstone, limestone, 

 shale, etc., which sometimes measure hundreds of feet in tiiickness. The 

 study of the floras of our time does not afford us any data in regard to the 

 duration of vegetable types. The human races are still too young, or at 

 least the records of the present vegetation do not yet reach far enougli to 

 afford evidence of the modification of any species of plants. AVe have, 

 however, positive facts in the more recent geological times which prove a 

 remarkable degree of persistence in the characters of a flora for a distance 

 of time, as indicated by interstratified formations, still longer than it may 

 be supposed necessary' fbr the production of tsvo coal beds, and hundreds 

 of feet of shale, sandstone, etc. between them. In the Tertiary of the 

 Rocky Mountains, strata bearing jdants in connection with lignites have 

 been found at Point of Rocks, Wyoming Territory, and a number of 

 identical species, indeed, a flora bearing the same general characters, is 

 exposed, also with lignite beds, at Black Butte, though the two localities 

 are separated by tliree to four thousand feel of measures, shale, sandstone, 

 lignite beds, etc. If these lignite floras had been considered separately 

 and without evidence of the distribution of the intervening measures, tliey 

 would have bet-n admitted as evidently synchronous, or as representing 

 the same horizon. Hence the long persistence of vegetable t3'pcs is a fact 

 which lias to be recognized by paleontologists although it may be contra- 

 dictory to theoretical considerations. 



The modifications in the characters of the plants are recognized, how- 

 ever, in the flora of the Carboniferous; but they have been slow, Iran- 



